Field of the Invention
The present invention relates to an image sensor and an image capturing apparatus using the image sensor.
Description of the Related Art
The number of pixels in a CMOS image sensor in a recent digital camera has been increasing, whereas there is also an increasing need for the image sensing in which an image with a high-number of pixels is output at a high frame rate, as in the case of a Full HD moving image which is a 1920×1080 image output at 30 fps or 60 fps, for example.
With regard to this need, thinning processing is known as a method for reducing in the number of pixels in order to achieve the image sensing at a high frame rate using a CMOS image sensor having a high-number of pixels. In the thinning processing, the number of pixels is decreased by performing drive control so as not to read out signals from pixels in a given cycle, and an increase in the frame rate is achieved by reducing the data rate. Since signals are not read out from pixels in a given cycle in this processing, a captured image has characteristics, that is, the image is advantageous in edge detection for a subject, but meanwhile, moiré, which is a kind of folding noise, tends to stand out.
As a method for reducing moiré, some methods have been proposed in which a signal of a pixel that is not read out in the thinning processing is merged with a signal of an adjoining signal to decrease the number of pixels, and the merged signal is output. In pixel merging processing disclosed in Japanese Patent Laid-Open No. 2010-259027, processing for merging pixel signals from a plurality of rows is performed by simultaneously selecting a plurality of rows using a row selection circuit, and simultaneously outputting signals from the plurality of selected rows. With the above method, an effect of reducing moiré and causing random noise to converge is achieved by obtaining merged output of the plurality of pixels. Due to this effect, in general, the pixel merging processing in which pixel signals are merged in a CMOS image sensor to decrease the number of pixels is superior to simple thinning processing, in terms of image quality.
However, with the pixel merging processing, the edge of a subject blurs, resulting in an image with low perceived resolution.